China builds a SOSUS.

China is planning to build a massive underwater observation system across the disputed East and South China seas, that experts say could be used to detect the movement of foreign ships and diminish the stealth capabilities of US submarines. According to state-run broadcaster CCTV, the monitoring networks will cost two billion yuan ($290 million) and “serve as a platform to provide long-term observation data and support experiments in the research of the maritime environments of the two seas.” … “An ocean power must be able to go to the high seas and go global,” he said. His colleague Zhou Huaiyang added the system could provide benefits to “national defense.” Thayer said China “could use the cover story for this undersea network to lay sensors designed to detect the movement of surface warships and submarines in particular.” Such a system, said Thayer, “mitigates the steal...